Various copper alloys have excellent electrical conductivity and excellent workability and, therefore, have been used for various electronic components and mechanical components. Regarding such copper alloys as well, still more improvement in workability has been required to make products more compact and extend the functionality. In order to work a copper alloy material into a fine member with high precision, it is desired that the copper alloy material is made into a rolled alloy by conducting rolling in such a way as to become a state in which good workability is ensured. For example, it is known that (111) orientation in parallel to a sheet surface, that is, development of a <111>//ND texture is important for improving the press formability and workability in bending (Non-Patent Documents 1 and 2). Regarding metals, e.g., aluminum and copper, having a face centered cubic (FCC) structure, it is known that this <111>//ND component is not developed by a common rolling and annealing method but is developed by shear deformation. For example, <111>//ND is developed in the vicinity of the surface of aluminum rolled under a high friction (Non-Patent Document 3).
It is believed that differential speed rolling is useful for development of a <111>//ND texture throughout the sheet thickness, and the usefulness for an aluminum alloy sheet has been reported (Non-Patent Document 4). On the other hand, it has been reported that when oxygen-free copper and brass, which is a copper-zinc alloy, are subjected to working through differential speed rolling, a <111>//ND texture is formed throughout the sheet thickness (Non-Patent Document 5).    Non-Patent Document 1: Ph. Lequeu and J. J. Jonas: Metallugical transactions A, 19A (1988), 105-120    Non-Patent Document 2: I. Gokyu, K. Suzuki, and C. Fujikura, J. Japan Inst. Metals, 32 (1968), 742-747    Non-Patent Document 3: T. Sakai, S. H. Lee and Y. Saito, Proc. LiMAT2001, Busan, Korea (2001), 311-316    Non-Patent Document 4: T. Sakai, K. Yoneda, Y. Saito, Material Science Forum, 396-412 (2002), 309-314    Non-Patent Document 5: T. Sakai, J. Watanabe, N. Iwamoto and H. Utsunomiya, Journal of the JRICu, Vol. 44 No. 1 (2005), 73-78